Gas damped deceleration switches which close an electrical circuit to activate an airbag inflator in a vehicle in response to vehicle deceleration are known. One such gas damped deceleration switch is shown in U.S. Pat. No. 4,536,629 wherein a mass is supported in a housing for movement in response to deceleration. The mass is spring biased into a rest position, and is movable against the bias of the spring toward an electrical contact. The electrical contact is movable by the mass to close an electrical circuit to energize an airbag inflator.
The mass is a rod-shaped member having a forward end and a rear end, and is supported for longitudinal movement in the housing. A spiral spring supported in the housing is coaxially connected to the mass at a position adjacent to the forward end of the mass. The rear end of the mass is supported in a bore formed in the rear wall of the housing, and is slidably movable in the bore. A damping member is connected to the mass adjacent to the rear end of the mass and is movable with the mass.
Movement of the mass from its rest position toward the electrical contact is resisted by damping forces exerted against the moving damping member. When in the rest position, the movable damping member is held in engagement with a flexible, stationary member to define an air space between the two members. As the movable damping member is carried by the mass away from the flexible stationary member, the space between the two members is enlarged. Enlargement of the space between the two members creates a vacuum within the space. The vacuum results in a pressure differential acting across the movable damping member. This pressure differential results in a damping force acting against the movable damping member which resists movement of the mass toward the electrical contact.
If the deceleration is of sufficient magnitude and duration, the mass will be moved against the damping force, as well as against the bias of the spiral spring, to carry the movable damping member away from the stationary member and to open the space between the two members. Thus, the vacuum in the space will no longer exist. Further movement of the mass and the moving damping member is resisted by the continuing bias of the spring and a minimal amount of damping force as required to displace the air around the moving damping member. If the deceleration is not of sufficient magnitude and duration to cause the moving mass to overcome the damping forces, the mass and the movable damping member will be moved back into the rest position by the bias of the spiral spring.
Vehicles are known to experience decelerating crash pulses having force components which act in directions transverse to the direction of movement of the vehicle, as well as in directions aligned with the direction of movement of the vehicle. A deceleration switch may thus be subjected to crash forces which are not directed entirely along the axis of the deceleration switch. An axial component of such a crash force will urge the mass to move only along the axis of the deceleration switch, but transverse components of such a crash force will urge the movable mass to move transversely off of the axis of the deceleration switch.